1. Field of the Invention
This invention relates to the preparation of novel surfactants and their utilization in producing cellular foam materials, particularly phenolic foams. The surfactants are prepared by reacting under free radical polymerization conditions a polyoxyalkylene adduct, a cyclic nitrogenous vinyl monomer and an esterified unsaturated dibasic acid in the presence of an organic or inorganic per-compound and a metal catalyst.
2. Description of the Prior Art
Phenolic polymers have been known for decades. More recently there has been increased interest in phenolic polymers which can be formed into cellular materials more commonly referred to as foams. These foams are produced by mixing reactants in the presence of a blowing agent. See, for example, Thomas et al. U.S. Pat. No. 2,744,875 (1956); Nelson Canadian Pat. No. 674,181 (1963); Dijkstra Canadian Pat. No. 684,388 (1964); Wissenfels et al. Canadian Pat. No. 866,876 (1971); United Kingdom Specification No. 598,642 (1948); Australian Pat. No. 128,508 (1945); and Modern Plastics Encyclopedia, Volume 41, pages 362,363 (1964). However, most known cellular materials produced from phenolic polymers exhibit an unsatisfactory thermal conductivity initially. Other known cellular materials produced from phenolic polymers exhibit an undesirable increase in thermal conductivity with time.
U.S. Pat. No. 4,140,842 (1979) discloses improved phenolic foam materials made with phenol:o-cresol resoles, which are characterized by high thermal resistance and a relatively slow increase in thermal conductivity with time. These foams are produced utilizing a cell stabilizing surfactant which is the capped reaction product of an alkoxylated amine and a copolymerizable mixture of dialkyl maleate and N-vinyl-2-pyrrolidinone or N-vinyl caprolactam. The latter co-monomers are polymerized with a combination of the initiators azobisisobutyronitrile and t-butyl-perbenzoate. A disadvantage of these phenolic foams is that at higher phenol:o-cresol ratios, i.e., a deficiency of o-cresol, the cellular material produced tends to become coarse celled and too friable.